Automatic transmissions for motorized vehicles necessarily utilize a continuous interior circulation of oil. As a consequence, the oil is used over and over. Over the years, such automatic transmissions have gradually diminished in size and the oil pumps thereof likewise have become smaller. As a consequence, it is important that the supply of oil which is available therein be utilized efficiently. With the larger pumps, there was a sufficient supply of oil furnished so that parts of the transmission were supplied with more oil than was actually needed. In recent years, however, such excess flow of oil is needed elsewhere within the interior of the transmission.
One such area of the automatic transmission where an excess flow has been provided is that between the tubular front bearing and the main shaft. The main shaft is driven by the torque converter and the front bearing is located at the end of that shaft. The conventional front bearing is installed within a metal sleeve by means of a press-fit and it surrounds the main shaft, to confine a flow of the oil in the space between its interior wall surface and the circumferential surface of the rapidly rotating main shaft. The main shaft rotates at an extremely high rate of speed and, consequently, generates high temperatures over a wide range of approximately -40.degree. F. to 300.degree. F. Such shafts rotate in the neighborhood of up to 7,000 revolutions/minute and have a surface speed of approximately 3,200 feet/minute. The flow of oil therearound can be thought of as an oil-bearing. In the form of transmission shown herein, once the oil flows past the front bearing, it is returned to the pan from which it is recirculated. If the flow becomes inadequate, there is danger of a " lock-up" between the main shaft and the surrounding front bearing, which would destroy the automatic transmission. The exact amount of oil-flow required to maintain the front bearing in "live" condition has not been determined. A "live" condition is defined as conditions under which there is sufficient oil-flow to enable the front bearing and oil to function as a bearing for the main shaft.
Until recently the flow of oil between the front bearing and the main shaft was approximately 2-4 liters/minute. The volume of oil-flow through the front bearing varies with the temperature of the oil because the viscosity of the oil decreases as the temperature rises, which causes the oil-flow rate to rise, everything else being equal. A flow of 2-4 liters/minute exceeds the amount of oil-flow which is required, and the engineers are seeking to restrict the flow and re-direct the excess to other parts of the transmission where it is needed. As a consequence, I was requested to design a method of partially restricting the flow of oil between the main shaft and the front bearing so that the excess could be utilized elsewhere. It was estimated by the engineers that the flow should be reduced to 0.7 liter-1.5 liters/minute.
The engineers informed me that they had unsuccessfully sought to utilize an elastomeric ring to control the oil-flow, but to no avail. A thermoplastic ring maintains a consistent resistance to oil over a broad range of temperatures. An elastomer cannot maintain a consistent modulus over the broad temperature range to which a transmission is subjected. In addition, one cannot achieve a controlled flow with the modular change of the elastomer.
When I proposed the thermoplastic ring which is the subject matter of this application, the engineers laughed at the prospect. We have found, however, that with such a thermoplastic ring when manufactured and installed properly, and with an appropriate gap size, the flow is controllable and will be reduced to the desired levels while still providing a controlled flow which is adequate to maintain the bearing in a condition such that it can perform its intended function.
Similar split rings have been utilized previously in a groove or gland, but only under conditions such as to attempt to maintain a complete seal, so as to prevent any flow of oil thereby. We know of no instance where such a ring has been used to provide a continuous controlled flow, or for any purpose where the ring has been installed under the conditions and in the manner and location which we prescribe herein. These conditions, as will be shown hereinafter, are essential to the proper function of the ring to provide a controlled flow through the bearing and past the main shaft.